The research goals of Project 3 are to investigate strategies for the treatment of cryptosporidiosis based on the inhibition of parasite attachment and cell invasion by monoclonal IgAs directed against sporozoite surface epitopes. Attention will be focused on developing and characterizing monoclonal IgA antibodies against surface epitopes shared by exogenous (sporozoites) and endogenous (merozoites) infectious forms to maximize the efficiency of inhibition. Specific Aim 1 will be devoted to production and analysis of dimeric monoclonal IgA clones reactive against sporozoite and merozoite surface molecules. This work will be performed at Dr. Neutra's laboratory at the Children's Hospital, Harvard Medical School. Specific Aim 2 will demonstrate in animal models the ability of IgA clones to protect mice against Cryptosporidium infection. Hybridoma cells will be injected subcutaneously to produce IgA- secreting tumors (backpack). Cells will be injected to infant Balb/C mice, simultaneously challenged with Cryptosporidium oocysts to determine protection against infection, and to weaned SCID mice chronically infected to determine impact on clearing existing infection. The impact of an oral course of IgA antibodies will also be tested; monoclonal antibodies will be fed to infant mice simultaneously challenged with Cryptosporidium, and to weaned SCID mice chronically infected. A course of intravenous injections to SCID mice with evidence of hepato-biliary involvement will determine impact on Cryptosporidium infection of the biliary tree. This work will be performed jointly between Dr. Neutra's laboratory and Dr. Tzipori's at TUSVM, which are 30 miles apart. Specific Aim 3 will largely be performed at Dr. Flanigan's laboratory at Miriam Hospital, Brown University (50 miles distance). The nature of inhibition will be determined in cell culture system (HT29.74) developed by Dr. Flanigan. He will determine whether inhibition is caused by interference with, sporozoite binding, penetration, or development within the host cell. Project 3 is also responsible for program administration, and for providing services which include, i) production and regular supply of oocysts to all 3 projects, and ii) will be responsible for performing all animal challenge assays and analyses.